Definition from IAI: The space boundary defines the
physical or virtual delimiter of a space by the relationship
IfcRelSpaceBoundary to the surrounding elements.

In the case of a physical space boundary, the placement and
shape of the boundary may be given, and the building element,
providing the boundary, is referenced,

In the case of a virtual space boundary, the placement and
shape of the boundary may be given, but no building element is
referencedand a virtual element is
referenced instead.

The IfcRelSpaceBoundary is defined as an objectified
relationship that handles the element to space relationship by
objectifying the relationship between an element and the space it
bounds. It is given as a one-to-one relationship, but allows each
element (including virutal elements and openings) to define many
such relationship and each space to be defined by many such
relationships.

Space boundaries are always defined as seen from the space. In
general two basic types of space boundaries are
distinguished:

1st level space boundary: defined
as boundaries of the space, not taking into account any change in
building element or spaces on the other side.

2nd level space boundary: defined
as boundary taking any change in building element or spaces on
the other side into account. It can be further distinguished into

2nd level type A: There is a space
on the other side.

2nd level type B: There is a
building element on the other side.

The exact definition of how space boundaries
are broken down depends on the view definition, more detailed
conventions on how space boundaries are decomposed can only be
given at the domain or application type level.

In an architectural or FM related view, a space
boundary is defined totally from inside the space. This is a
1st level space boundary.

In a thermal view, the decomposition of the space
boundary depends on the material of the providing building
element and the adjacent spaces behind. This is a
2nd level space boundary.

1st level space boundary

2nd level space boundary

2nd level type A

2nd level type B

HISTORY New entity in
IFC Release 1.5, the entity has been modified in IFC Release
2x.

IFC2x PLATFORM CHANGE
The data type of the attributeRelatedBuildingElement has
been changed from IfcBuildingElement to its supertype
IfcElement. The data type of the attribute
ConnectionGeometry has been changed from
IfcConnectionSurfaceGeometry to its supertype
IfcConnectionGeometry.
IFC2x4 CHANGE The attribute RelatedBuildingElement has
been made mandatory. For virtual boundaries the reference to
IfcVirtualElement is now
mandatory.

Attribute Use Definitions

The differences between the 1st and
2nd level space boundaries is
identified by:

If the IfcRelSpaceBoundary is used to express a virtual
boundary, the attribute PhysicalOrVirtualBoundary has to
be set to VIRTUAL. The attribute RelatedBuildingElement
shall point to an instance of IfcVirtualElement. If the
correct location is of interest, the attribute
ConnectionGeometry is required.

NOTE The connection geometry, either by a 2D
curve or a 3D surface, is used to describe the portion of the
"virtual wall" that separates the two spaces. All instances of
IfcRelSpaceBoundary given at the adjacent spaces share the
same instance of IfcVirtualElement. Each instance of
IfcRelSpaceBoundary provides in addition the
ConnectionGeometry given within the local placement of
each space.

If the IfcRelSpaceBoundary is used to express a
physical boundary between two spaces, the attribute
PhysicalOrVirtualBoundary has to be set to PHYSICAL. The
attribute RelatedBuildingElement has to be given and
points to the element providing the space boundary. The attribute
ConnectionGeometry may be inserted, in this case it
describes the physical space boundary geometically, or it may be
omited, in that case it describes a physical space boundary
logically.

Geometry Use Definitions:

The IfcRelSpaceBoundary may have geometry attached. If
geometry is not attached, the relationship between space and
building element is handled only on a logical level. If geometry
is attached, it is given within the local coordinate systems of
the space.

NOTE: The attributes
CurveOnRelatingElement at
IfcConnectionCurveGeometry or
SurfaceOnRelatingElement at
IfcConnectionSurfaceGeometry provide the geometry within
the local coordinate system of the IfcSpace, whereas the
attributes CurveOnRelatedElement at
IfcConnectionCurveGeometry or
SurfaceOnRelatedElement at
IfcConnectionSurfaceGeometry provide the geometry within
the local coordinate system of the subtype of
IfcElement.NOTE In most view definitions the connection geometry for
the related IfcElement is not
provided.

The geometric representation (through the
ConnectionGeometry attribute) is defined using either 2D
curve geometry or 3D surface geometry for space boundaries. In
most view definitions the 3D connection surface geometry is
required.

1st level space boundary:

only connection geometry for related space shall be
provided

only surface connection geometry shall be provided

only the following surface representations are supported:

IfcSurfaceOfLinearExtrusion

IfcCurveBoundedPlane

IfcCurveBoundedSurface

IfcFaceBasedSurfaceModel

2nd level space boundary:

only connection geometry for related space shall be
provided

only surface connection geometry shall be provided

only the following surface representations are supported:

IfcCurveBoundedPlane with restrictions to have
polygonal boundaries only

IfcFaceBasedSurfaceModel

Surface connection geometry

The following constraints apply to the surface connection
geometry representation:

planar boundaries:

IfcSurfaceOfLinearExtrusion defined by a
SweptCurve being an IfcArbitraryOpenProfileDef with
straight segements, or

IfcCurveBoundedPlane

curved boundaries

IfcSurfaceOfLinearExtrusion defined by a
SweptCurve being an IfcArbitraryOpenProfileDef with
curves segements, or

IfcCurveBoundedSurface with a BasisSurface
being a non planar surface, such as IfcCylindricalSurface,
or

((PhysicalOrVirtualBoundary = IfcPhysicalOrVirtualEnum.Physical)
AND (NOT('IFCPRODUCTEXTENSION.IFCVIRTUALELEMENT' IN TYPEOF(RelatedBuildingElement))))
OR
((PhysicalOrVirtualBoundary = IfcPhysicalOrVirtualEnum.Virtual)
AND (('IFCPRODUCTEXTENSION.IFCVIRTUALELEMENT' IN TYPEOF(RelatedBuildingElement))
OR ('IFCPRODUCTEXTENSION.IFCOPENINGELEMENT' IN TYPEOF(RelatedBuildingElement))))
OR
(PhysicalOrVirtualBoundary = IfcPhysicalOrVirtualEnum.NotDefined);

IFC2x PLATFORM CHANGE The data type has been changed from IfcBuildingElement to IfcElement with upward compatibility for file based exchange.
IFC2x4 CHANGE The attribute has been changed to be mandatory.

ConnectionGeometry

:

Physical representation of the space boundary. Provided as a curve or surface given within the LCS of the space.

IFC2x PLATFORM CHANGE The data type has been changed from IfcConnectionSurfaceGeometry to IfcConnectionGeometry with upward compatibility for file based exchange.

If the space boundary is physical, it shall be provided by an element (i.e. excluding a virtual element). If the space boundary is virtual, it shall either have a virtual element or an opening providing the space boundary. If the space boundary PhysicalOrVirtualBoundary attribute is not defined, no restrictions are imposed.

IFC2x4 CHANGE Where rule corrected to accept an IfcOpeningElement for a virtual space boundary.